The present invention relates generally to Digital Subscriber Loop (DSL) technology, and specifically to a system and method for effectively providing an increased bandwidth and increased reliability.
One proposal for high-speed communication is the introduction of Digital Subscriber Line (DSL) technology. Currently, there many different DSL standards, including Asymmetric DSL (ADSL), High-speed DSL (HDSL), Very High Speed DSL (VDSL), Symmetric DSL (SDSL), Symmetric, High-speed DSL (SHDSL), Integrated Services Digital Network (ISDN) DSL (IDSL) systems, and the like. Generically, the term DSL is used to represent these, and other, standards. One of the most attractive features of DSL is that it is implemented using an infrastructure that already exists, namely the Plain Old Telephone System (POTS). DSL shares copper twisted pair lines typically used for telephone communication.
However, there are still several issues with DSL technology. A first issue is the lack of protection of DSL line cards due to cost implications, and due to the fact that a single or low number of customer(s) may be impacted. For example, failure of a DSL line caused by a cut wire results in loss of service only to the customer serviced by the line. To overcome this protection limitation, carriers often include a redundant DSL line in their offering to businesses or other customers demanding carrier-grade service. However, from an end-user perspective, this type of fail-over recovery mechanisms may not be economically viable. This expense results because the redundant DSL line carries no additional bandwidth. Additionally, the customer may need to add router(s) to their network, which complicates the provisioning and adds cost to the operations of the network. Yet further, the recovery from a defective line to the redundant, back-up line may also be slow.
A second issue with DSL technology is bandwidth limitation. DSL has a known rate/reach limitation. Generally, a longer line obtains a lower bandwidth service than a shorter line. Also, a poor quality line, for example a bad cable or a line with taps, will obtain a lower bandwidth service than a high quality line. Such line impairments limit the ability of a carrier to offer services having high bandwidth requirements, for example video.
Higher speed, layer-1 solutions, such as VDSL instead of ADSL, attempt to address the bandwidth problem but may suffer from a high initial deployment cost. Typically, VDSL line cards are more expensive, less dense, and have worse rate/reach limitations than ADSL. Additionally, fixing the physical line to the customer by removing taps and/or bridges on the line may improve the bandwidth available on the line, but a service call of this nature is very expensive, and the required bandwidth may still not be achieved.
To address the above issues, a number of solutions are currently proposed by the industry. A “layer 1” solution can be provided to address the bonding of two lines. Bonding at layer 1 ties two or more lines together at the physical layer. A simple example is bitwise or bytewise multiplexing of the bits or bytes from two or more lines together. An example of layer 1 bonding is given in the BONDING specification from Integrated Services Digital Network (ISDN).
A layer 1 solution is elegant because it hides the plurality of lines from upper layers. However, it tends to be inflexible in parameters like different link lengths, delay between lines, and different link rates. Also, bonding tends to be implemented on one chip, or one circuit card (line card), due to the tight coupling of the lines bonded together. Thus, a layer 1 solution does not address the issue of line card failure. Further, it typically cannot address the bonding of more lines than fit on one chip or one line card, nor does it address lines that are operating at different rates.
A “layer 2” solution can be implemented instead of, or in addition to, the layer 1 solution. An example of a layer 2 solution for Asynchronous Transfer Mode (ATM) is Index Multiplexing over ATM (IMA). IMA bundles multiple physical links to create a bigger virtual link. However, IMA requires underlying physical links to be of the same speed, or bandwidth, which limits the granularity of the service offerings. That is, as applied to DSL, every DSL line must be of equal speed.
Another example of a layer 2 solution is a Point-to-Point Protocol (PPP) solution. In the PPP solution, multi-line PPP (MP) can bond lines together. RFC 1717, written in 1994, defines Multilink PPP, which is now used in virtually all modem ISDN equipment. It was later replaced by RFC 1990. Multilink PPP allows ISDN devices to bond two 64K channels into a logical 128K channel. This solution is effective because it can bond together lines of different rates and delays. However, it relies on data being on top of PPP. Many protocols do not support PPP, which limits the scope of application of such a solution.
Yet a further solution is to implement a “layer 3” solution, such as routing data across two or more DSL lines to the same customer. While this solution does a good job for load balancing across multiple flows, it cannot split a single traffic flow across multiple links. That is, a largest flow supported by this solution depends on the bandwidth of the largest DSL links. Additionally this solution can suffer from the following issues. It is expensive due to two ADSL routers, two gateway devices, and an additional service provider supplied router. Layer 3 recovery can be slow. Multiple layer 3 routes can cause network confusion. Multiple layer 3 routes can cause return path route asymmetry.
Thus it can be seen that the current solutions are effective for either addressing issues of protecting a DSL line or reducing bandwidth limitations, but not both. Furthermore, the current solutions may be impractical, expensive or complicated. Thus, it is an object of the present invention to obviate or mitigate at least some of the above-mentioned disadvantages.